Genetic Drift Random changes in allele frequency. Will occur faster in small populations NOT the same as Natural Selection (which is not random) The bottleneck and founder effects commonly cause populations small enough for genetic drift to be significant

Genetic drift faster in small population Large pool Small pool AA Aa aa Genetic drift faster in small population AA Aa aa AA Aa aa AA

Changes in allele frequencies In small populations, genetic drift operates quite quickly and new alleles can increase in frequency by chance. In larger populations, genetic drift is slower, and natural selection is more important in increasing the frequency of a new allele.

Founder Effect Bottleneck Effect Small group of individuals move away from the main population. Eg a group of insects blown by wind to a small island Bottleneck Effect Catastrophic events wipe out many individuals. Eg avalanche, volcanic eruption

Original large population has equal proportions of blue and red A small founder population may be separated from the parent population

Mutant has established in the new population AA AA AA AA AA AA AA AA AA AA Aa AA AA Aa Aa AA AA AA AA AA AA AA AA AA AA AA AA AA AA AA Aa AA Aa AA Aa Aa AA Aa AA AA AA AA AA AA AA AA Aa AA AA Parent population has a single mutant AA Aa AA Aa AA AA AA AA AA A catastrophe wipes out most of the parent population Aa Aa AA AA AA AA AA Aa

Genetic drift RANDOM CHANGES IN GENE POOL Occurs over time Faster in small populations Without other factors Genetic drift will eventually lead to the extinction of one allele RESULT: Change in allele frequencies

Founder & Bottleneck effects Founder effect – small population of pioneers Bottleneck effect – small population due to catastrophe Founder effect and bottleneck effect both cause an immediate change in allele frequency + small population is more prone to genetic drift RESULT: Change in allele frequencies